Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for processing seismic data sets that are recorded with different spatial sampling and different temporal bandwidths.
Discussion of the Background
Reflection seismology is a method of geophysical exploration to determine the properties of a portion of a subsurface layer in the earth, information that is especially helpful in the oil and gas industry. Marine reflection seismology is based on the use of a controlled source that sends energy waves into the earth. By measuring the time it takes for the reflections to come back to plural receivers, it is possible to estimate the depth and/or composition of the features causing such reflections. These features may be associated with subterranean hydrocarbon deposits.
For marine applications, a seismic survey system 100, as illustrated in FIG. 1, includes a vessel 102 that tows plural streamers 110 (only one is visible in the figure) and a seismic source array 130. Streamer 110 is attached through a lead-in cable (or other cables) 112 to vessel 102, while source array 130 is attached through an umbilical 132 to the vessel. A head float 114, which floats at the water surface 104, is connected through a cable 116 to the head end 110A of streamer 110, while a tail buoy 118 is connected, through a similar cable 116, to the tail end 1106 of streamer 110. Head float 114 and tail buoy 118 are used, among other things, to maintain the streamer's depth. Seismic sensors 122 are distributed along the streamer and configured to record seismic data. Seismic sensors 122 may include a hydrophone, geophone, accelerometer or a combination thereof. Positioning devices 128 are attached along the streamer and controlled by a controller 126 for adjusting a position of the streamer according to a survey plan.
Source array 130 has plural source elements 136, which are typically air guns. The source elements are attached to a float 137 to travel at desired depths below the water surface 104. During operation, vessel 102 follows a predetermined path T while source elements (usually air guns) 136 emit seismic waves 140. These waves bounce off the ocean bottom 142 and other layer interfaces below the ocean bottom 142 and propagate as reflected/refracted waves 144, which are recorded by sensors 122. The positions of both source elements 136 and recording sensors 122 may be estimated based on GPS systems 124 and recorded together with the seismic data in a storage device 127 onboard the vessel. Controller 126 has access to the seismic data and may be used to achieve quality control or even fully process the data. Controller 126 may also be connected to the vessel's navigation system and other elements of the seismic survey system, e.g., positioning devices 128.
Alternatively, the seismic data may be collected in a land environment as illustrated in FIG. 2. According to this scenario, a seismic acquisition system 200 includes plural receivers 202 positioned over an area 204 of a subsurface to be explored and in contact with, or below the surface 206 of, the ground. A number of dedicated seismic sources 208 are also placed on the surface 206 in an area 210, in a vicinity of the area 204 of the receivers 202. Note that a dedicated seismic source is defined as a device built by man with the main purpose of generating seismic waves to be used for a seismic survey. Alternatively, dedicated seismic sources 208 may be buried under surface 206. A central recording device 212 is connected to the plurality of receivers 202 and placed, for example, in a station/truck 214. Each dedicated seismic source 208 can be composed of a variable number of vibrators, typically between one and five, and can include a local controller 216. A central controller 218 can be provided to coordinate the shooting times of sources 208. A global positioning system (GPS) 220 can be used to time-correlate shooting of the dedicated seismic sources 208 and the recordings of the receivers 202. With this configuration, dedicated seismic sources 208 are controlled to intentionally generate seismic waves, and the plurality of receivers 202 records waves reflected by oil and/or gas reservoirs and other structures.
Both in the land and marine seismic acquisition data, there are cases when two different sets of seismic data are acquired over the same desired subsurface. These two sets of seismic data are combined when generating an image of the subsurface. Traditionally, the data combination is possible because the two sets of seismic data are acquired to have the same spatial sampling, i.e., the data is recorded at the same locations, as schematically illustrated in FIG. 3A, where the first set of seismic data 300 is represented by circles and the second set of seismic data 302 is represented by crosses. Note that parameters 1 and 2 on the X and Y axes in FIG. 3A may be any of the x, y and z coordinates. However, it is possible that two sets of seismic data 310 and 312 have a different spatial sampling, as illustrated in FIG. 3B. If this is the case, existing seismic processing methods and algorithms are not capable of combining the two sets of seismic data. If the two seismic data sets further have different temporal bandwidths, in addition to different spatial sampling, then most traditional algorithms are not capable of processing this data.
Thus, there is a need to develop new algorithms and methods for processing seismic data sets having different spatial sampling and different temporal bandwidths.